236,085 research outputs found
Single-bubble and multi-bubble cavitation in water triggered by laser-driven focusing shock waves
In this study a single laser pulse spatially shaped into a ring is focused
into a thin water layer, creating an annular cavitation bubble and cylindrical
shock waves: an outer shock that diverges away from the excitation laser ring
and an inner shock that focuses towards the center. A few nanoseconds after the
converging shock reaches the focus and diverges away from the center, a single
bubble nucleates at the center. The inner diverging shock then reaches the
surface of the annular laser-induced bubble and reflects at the boundary,
initiating nucleation of a tertiary bubble cloud. In the present experiments,
we have performed time-resolved imaging of shock propagation and bubble wall
motion. Our experimental observations of single-bubble cavitation and collapse
and appearance of ring-shaped bubble clouds are consistent with our numerical
simulations that solve a one dimensional Euler equation in cylindrical
coordinates. The numerical results agree qualitatively with the experimental
observations of the appearance and growth of bubble clouds at the smallest
laser excitation rings. Our technique of shock-driven bubble cavitation opens
novel perspectives for the investigation of shock-induced single-bubble or
multi-bubble cavitation phenomena in thin liquids
The effects of a comptonizing corona on the appearance of the reflection components in accreting black hole spectra
We discuss the effects of a comptonizing corona on the appearance of the
reflection components, and in particular of the reflection hump, in the X-rays
spectra of accreting black holes. Indeed, in the framework of a thermal corona
model, we expect that part (or even all, depending on the coronal covering
factor) of the reflection features should cross the hot plasma, and thus suffer
Compton scattering, before being observed. We have studied in detail the
dependence of these effects on the physical (i.e. temperature and optical
depth) and geometrical (i.e. inclination angle) parameters of the corona,
concentrating on the slab geometry . Due to the smoothing and shifting towards
high energies of the comptonized reflection hump, the main effects on the
emerging spectra appear above 100 keV. We have also investigated the importance
of such effects on the interpretation of the results obtained with the standard
fitting procedures. We found that fitting Comptonization models, taking into
account comptonized reflection, by the usual cut-off power law + uncomptonized
reflection model, may lead to an underestimation of the reflection
normalization and an overestimation of the high energy cut-off. We discuss and
illustrate the importance of these effects by analysing recent observational
results as those of the galaxy NGC 4258. We also find that the comptonizing
corona can produce and/or emphasize correlations between the reflection
features characteristics (like the iron line equivalent width or the covering
fraction) and the X-ray spectral index similar to those recently reported in
the literature. We also underline the importance of these effects when dealing
with accurate spectral fitting of the X-ray background.Comment: 11 pages, 14 figures accepted for publication in MNRAS. Version
printable on US 8.5x11 pape
Robust visualization and discrimination of nanoparticles by interferometric imaging
Single-molecule and single-nanoparticle biosensors are a growing frontier in diagnostics. Digital biosensors are those which enumerate all specifically immobilized biomolecules or biological nanoparticles, and thereby achieve limits of detection usually beyond the reach of ensemble measurements. Here we review modern optical techniques for single nanoparticle detection and describe the single-particle interferometric reflectance imaging sensor (SP-IRIS). We present challenges associated with reliably detecting faint nanoparticles with SP-IRIS, and describe image acquisition processes and software modifications to address them. Specifically, we describe a image acquisition processing method for the discrimination and accurate counting of nanoparticles that greatly reduces both the number of false positives and false negatives. These engineering improvements are critical steps in the translation of SP-IRIS towards applications in medical diagnostics.R01 AI096159 - NIAID NIH HHSFirst author draf
An investigation of film wavy structure in annular flow using two simultaneous LIF approaches
The paper is devoted to development and validation of film thickness measurement techniques in interfacial gas-liquid flows. The specific flow investigated here is that of downwards (co-flowing) annular flow in a vertical pipe, however, many of the observations and findings are transferable to similar flow geometries. Two advanced spatially resolved techniques, namely planar laser-induced fluorescence and brightness-based laser-induced fluorescence , are used simultaneously in the same area of interrogation. A single laser sheet is used to excite fluorescence along one longitudinal section of the pipe, and two cameras (one for each method) are placed at different angles to the plane of the laser sheet in order to independently recover the shape of the interface along this section. This allows us to perform a cross-validation of the two techniques and to analyse their respective characteristics, advantages and shortcomings
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